The present invention relates to a pressure relief device for nuclear containments that protects against severe over-pressurization and ultimate failure of nuclear reactor containments.
Nuclear power plants must be designed to ensure that even in the event of accidents, a mechanism will be provided to prevent or minimize the escape of radioactive material and noble gases. To guard against radioactive releases, the reactor system is typically housed within a containment structure that is constructed from steel and reinforced concrete. Thus the containment is capable of withstanding large pressures which may result from various accidents. However, it has been postulated that in severe accidents, the containment vessel itself could fail from gradually increasing over-pressurization. Although the likelihood of such an event is very small, the health risks associated with exposing the surrounding population to the radioactive releases of such an event has led many to believe that a mechanism should be provided to vent the containment structure at or somewhat above the design pressure and to filter the gases released. That is, it is desirable to both provide a pressure release device for the containment vessel and a mechanism for scrubbing any gases that may be released by the containment before they are released into the atmosphere.
To date there have been a wide variety of attempts to provide pressure relief devices for containment structures and/or scrubbers that remove a large percent of the radioactive material from the vented gases before they are released into the atmosphere. For example, in U.S. Pat. No. 3,889,707, Fay, et al. disclose a pressure relief and secondary containment system for preventing the release of radioactive gases. However, such a device has many drawbacks. Initially, the system is completely sealed. In the event of a large pressure increase within the primary containment, a pressure regulator fluid seal is breached, thereby allowing gases to escape into a second containment structure. However, such a system is only capable of storing (and not dissipating) energy, and in effect, works only as a larger containment vessel. Therefore, the device disclosed by Fay is inherently limited by its size. Further, the disclosed system requires extensive modification of existing plants and no provision is made for vacuum relief in the event that the containment vessel experiences a vacuum condition after an original high pressure transient.
U.S. Pat. No. 4,610,840 issued to Leach discloses a fission products scrubbing system for a nuclear reactor. Specifically, a secondary compartment in fluid communication with the containment is partially filled with water. In the event of a large pressure increase, a rupture disk disposed within a vent pipe emanating from the secondary compartment bursts to relieve pressure. When the rupture disk blows, radioactive gases and vapors from the containment pass through the water filled secondary compartment and are then released through the now open vent pipe. As the hot containment gases and vapors (primarily steam) pass through the water stored within the enclosed secondary compartment, a large majority of the fission products will be scrubbed from the containment gases. Therefore, the gases are released from the secondary compartment in a substantially purified state. While such a system reduces the radioactivity of the materials released, once the rupture disk has been broken, the system will not seal itself and thus substantially all of the gases within the containment vessel will escape even after a brief pressure transient.
In U.S. Pat. Nos. 3,865,688, 4,050,983, 4,210,614, and 4,473,528, Kleimola discloses various embodiments of passive containment systems for protecting against loss of coolant accidents in pressurized water or boiling water type nuclear reactors. The passive containment system described consists of plurality of interconnected cells, each housing a major component of the reactor. In the event of a loss of coolant accident, the containment system attempts to absorb all of the energy released by the nuclear fuel. While such an arrangement may possibly serve to protect against any loss of coolant accident, the proposed solution requires a complete redesign of present nuclear reactors and would be far more complex and costly than desired.